Fuel cells provide electricity from chemical oxidation-reduction reactions and possess significant advantages over other forms of power generation in terms of cleanliness and efficiency. Typically, fuel cells employ hydrogen as the fuel and oxygen as the oxidizing agent. The power generation is proportional to the consumption rate of these reactants.
A significant disadvantage which inhibits the wider use of fuel cells is the lack of a widespread hydrogen infrastructure. Hydrogen has a relatively low volumetric energy density and is more difficult to store and transport than hydrocarbon fuels currently used in most power generation systems. One way to overcome this difficulty is the use of reformers to convert a hydrocarbon fuel to a hydrogen rich gas stream that can be used as a feed for fuel cells.
Hydrocarbon-based fuels, such as natural gas, LPG, gasoline, and diesel, require conversion processes to be used as fuel sources for most fuel cells. Current art uses multi-step processes combining an initial conversion process with several clean-up processes. The initial process is most often steam reforming (SR), autothermal reforming (ATR), catalytic partial oxidation (CPOX), or non-catalytic partial oxidation (POX) or combinations thereof. The clean-up processes are usually comprised of a combination of desulphurization, high temperature water-gas shift, low temperature water-gas shift, selective CO oxidation, selective CO methanation or combinations thereof. Alternative processes for recovering a purified hydrogen-rich reformate include the use of hydrogen selective membrane reactors and filters.
A fuel cell produces water as a product of the electrochemical reaction that occurs in a fuel cell stack. Hydrogen-rich reformate produced by fuel processors as feed for a fuel cell typically contains water in liquid and vapor phases as a result of the fuel reforming process. Efficient operation of a fuel cell-fuel processing system depends on the ability to provide effective water management in the system and specifically to control the recovery of water in the system.
It is desirable to continually recover fuel cell product water so that it can be used for other purposes within the fuel cell system such as to provide water to the fuel processor. It is also desirable to minimize the amount of liquid water in the various system streams so as not to detrimentally effect reactors supplied by such streams. For example, liquid water should be eliminated from the fuel cell exhaust gases that are supplied to the combustor so as not to drown the combustor catalyst, or otherwise suppress combustion of the exhaust gases therein. Similarly, it is desirable to insure that the hydrogen-rich reformate gas stream supplied to the fuel cell contain little or no liquid water that could either drown the catalyst or flood the fuel cell and thereby reduce its effectiveness. Water is recovered from such streams differently depending on its physical state. When in liquid form, the product water is typically recovered by a mechanical water separator, and when in the vapor state, it is typically recovered by a condenser.
The present invention relates to mechanical water separators to recover liquid water from various process gas streams found in fuel cell and/or fuel processing systems. The design of a mechanical liquid water separator presents a tradeoff between separating efficiency, gas flow pressure drop, and physical volume. The objective is to maximize separating efficiency, minimize gas flow pressure drop, and minimize physical volume of the component. Maximum separating efficiency is desired so that sufficient product water is recovered. Minimal pressure drop is desired to minimize the power requirements in the system, thus increasing overall system efficiency. Minimum physical volume is desired so that the component may be easily packaged in a fuel processor system or integrated fuel cell-fuel processing system.